Rheostat



Feb. 28, 1928. 1,660,879

D. E. MOORE RHEOSTAT Filed March 19. 1923 Patented F eb. 28, 1928.

UNITED STATES PATENT OFFICE.

DANIEL E. MOORE, OF CHICAGO, ILLINOIS, ASSIGNOR TO CENTRAL RADIO LABORA- TORIES, A CORPORATION OF WISCONSIN.

BHEOS-TAT.

This invention relates to improvements in electrical devices and may be incorporated in a great variety of forms of electrical devices. I have here shown the invention embodied in two forms of rheostat tor the purpose of illustration. It is obvious, however, that without detracting from the spirit of the invention, the same may be embodied in other forms of rheostat, and, in fact, in other it; forms of electrical devices.

It wish to call attention to some of the features and advantages of the invention. Its use renders construction easy and simple, and cuts down the cost of production. An electrical device eii'ibodying the invention will be t'oiind to operate very easily and smoothly. The invention is especially valuable, in connection with a variable grid leak for radio apparatus. Such grid leaks are, in tact, rheoslats with an element having a very high resistance. By the use of my invention such a grid leak may be made using as a resistance elementji curved strip of paper or similar material coated on its surt'zue with ink. graphite, or other conducting material. The variations of resistance are obtained by passing the pointof contact over the surface of the resistance element. If this is done by ordinary rubbing frictional engagement, thev surface is usually daii'iaged as soon as the instrument has been used slightly. By the use of my invention, such a resistance element may be used indefinitely no matter how delicate its surface is. The point of contact is moved over the surface of the resistance element without any rubbing frictional engagement and consequently without any damage to the element. Also, by the use of my invention, a rheostat, such, for example, is ordinarily used in connection with radio tube filament control. may be easily and cheaply made. in such a rheostat it is usually desirable to use as a resistance element. a helical wire bent into the arc of a circle. Heretofore,

in making such a rlieostat, it has been diflicult to pass the point of contact over the turns of the helix without disturbing or distorting the same. Such rubbing contact over the turns of the helix also caused uneven and jerky operations. By the use of my invention such a helical resistance element may be Application filed March 19, 1923. Serial No. 6263124;

usedwitliout difficulty. It is not necessary to imbed the turns of the helix in cement in order to hold them in place, or otherwise 65 support them. The helix is merely laid in a circular groove or otherwise held in the requisite arcuate shape. It is not even necessary to wind the helix on a core or ribbon or other device as heretofore used, for the purpose of supporting the individual turns. The particular manner in which these advantages is accomplished by the use of my invention will appear more in detail hereinafter, and other features and advantages of my invention will become plain.

In those. forms of devices embodying the feature of my invention shown on the accompanying drawings, Figure 1 is a View in rear elevation of a'radio grid leak rheostat, Fig. 2 is a similar View in top plan, Fig. 3 ma view taken as indicated by the line 3 of Fig. 1. Fig. 4, is a view in elevation of another torm of rheostat such as is ordinarily used for radio tube filament control, Fig. 5 is a similar view in top plan, and Fig. 6 IS a view taken as indicated by the line 6 of Fig. l.

As shown in the drawings, 10 indicates an ordinary support or mounting such as a hard rubber panel as is frequently used in connection with radio apparatus. Mounted on the back of the support 10 is a curved strip of paper or other material 11, coated on its outer surface with graphite, ink, or other desirable conducting material 11". This strip of material, thus coated, forms the resistance element. It is supported by means of the two bolts 12 and 12*, one at each of its ends. These bolts 12 and 12*, are each provided with two nuts 13 and serve as binding posts in addition to supports for the resistance element.

The bolt 12 also supports one end of a curved strip of spring brass or other suitas able conducting material 15. This strip 15 is a conductor of exceedingly low resistance and is curved the same as the resistance element 11. The conductor 15, however, is sprung so that it does not lie in a plane. Its 00 normal shape is shown in Fig. 2, from which it will be noted that it normally does not contact with the resistance element 11 except at the end where it is held by the bolt 12".

This end lies on top of and in contact with the resistance element 11. The rest of the strip 15 stands away from and out of contact with the resistance element 11.

Centrally arranged with respect to the arcuate resistance element 11 is a shaft 19 passing through the panel -and provlded 1n front'of the panel with an indicating hand or pointer and an operating knob 20. This shaft 19 carries behind the panel a radlal arm 21 in contact with the conductor strip 15. The end of the arm 21 in contact with the strip holds such strip 15 agalnst the resistance element 11. Turning of the knob 20 serves to move the end of the arm 21 over the stri .15. As this occurs, the strip 15 is presse down into contact with the V resistance element 11 so that the portion of the strip 15 under the arm 21 is always in contact with the resistance element 11.

' The operation of the device can be easily understood. The wire connections are made tothe terminals 12 and-12. When the device is in the position shown in Fig. 2, with the arm 21 close to the terminal 12, the strip 15 is substantially entirely out of contact with the resistance element 11. When in upon what is used for the resistance element this position the current must flow through substantially the entire length of the resist ance element 11. When in this position the rheostat will give its maximum resistance. This-may be any amount desired depending 11. As the knob 20 is turned, the end of the "arm 21 moves over the strip- 15 pressing it into contact with the resistance element 11..

As has been stated, the strip 15 is; a very "good conductor, the resistance oiwhich is negligible. As the point of contact between the strip "15 and the resistance element 11 moves towards the terminal 12 it is obvious that the eflective length of the resistance element 11 will be shortened. In other words, a part of the resistance element 11 will be shortened or cut out by means of the conductor strip 15. This, obviously, will serve to lessen theresistance of the instrument.

It will be seen that the operation of the device causes no rubbing or frictional engement with the resistance element 11. onsequently, the coating of conductor material 11' may be made as thin and delicate as desired. There is no danger that this coating will be damaged, or rubbed off, in

using the device. The rubbin or frictional engagement occurs between t e end of the arm 21 and the metallic strip 15. The movementof the arm 21 over the strip 15 simply strip 15 an presses or In s it down on to the resistance element 11, t e point of contact moving with the end of the arm 21. There is no trictional engalgement or. rubbing between the the resistance element 11.

In that form of device illustrated in Figs.

4,5 and 6 I have shown a rheostat such as rea ers This rheostat does not have such a high resistance as the other one. I have here shown the resistance element as consisting of a hellcal wire 111. This wire is laid in a circular groove 111 which supports the same in arcuate shape. The ends of the resistance element 111 are held by means of bolts 112 and 112 similar to the bolts 12 and 12 of the other form of rheostat. The bolt 112 also supports one end of the strip 115 the same as the stri 15 in the other form of device. A sh t 119 with an indicating hand and operating knob 120 and an arm 121 are also provided which parts are the same as the parts 19, 20 and 21, respectively, in the other form of device. The operation of this rheostat is similar to that of the one just described and consequently need not be shown in detail. The movement of the end of the arm 121 serves to press the strip 115 into contact with the resistance element 111, I

the point of contact always lying under the end of the arm 121. Such operation serves to change the efiective length of the resistance element 111 and consequently vary the resistance as desired. Since there is no rubbing between the endof the arm 21 and the turns of the helix 111, the operation is smooth and even, and the turns of the helix 111 do not become dis laced or bent. The support given to the he ix at its ends by the bolts 112 and-112 and the groove 111' in which it lies are sufficient to hold it in position. In operation, the strip 115, is merely gently pressed into contact with the turns of the helix or laid down on it as the arm 121 moves.

While I have shown and described certain embodiments of my invention, it is to be all novelty inherent in my invention as' broadly as ossible in view of the prior art. What I c aim as new, and desire to secure by Letters Patent, is:

1. A device of the character described including an .electrical'conducting element of be made relatively high resistance lying in a lane, a

second normally spirally curved 'e ectrical conducting element of relatively low resistance having one of its ends in contact with one end of the first mentioned element, and

"means for bringing said second mentioned element into contact with the first mentioned element progressively throughout its length. 2. A device of the character described including an electrical conducting element of relatively high resistance lying in a plane,

a second normally spirally curved sprm electrical conducting element of relative y a second normally spirally curved electricalconducting element of relatively low resistance having one of its ends in contact with one end of the first mentioned element, said second mentioned element having the property of being brought into contact with the first mentioned element progressively throughout its length as pressure on it is moved throughout its length.

4. A device of the character described including an electrical conducting element of .relativel high resistance lying in a plane, a secon normally spirally curved springy electrical conducting element of relatively low resistance having one of its ends incontact with one end of thefirst mentioned element, said second mentioned element having the propert of being brought into contact with the rst mentioned element progressively throughout its length as pressure on it is moved throughout its length.

5. A device of the character described including an electrical conducting element of relatively high resistance lying in a plane, a second normally spirally curved electrical conducting element of relatively low resistance havin one of its ends attached and in cont-act wit one end of the first mentioned element, and means for pressing the second mentioned element into contact with the first mentioned element progressively throughout its length.

6. A device of the character described including an electrical conducting element of relativel high resistance lying in a plane, a .secon normally spirally curved springy electrical conducting element of relatively low resistance having one of its ends attached and in contact with one end of the first mentioned element, and means for pressing the second mentioned element into contact with the first mentioned element progressivel throughout its length.

evice of the character described including an electrical conducting element of contact wit relatively high resistance lying in a plane, a

second normally spirally curved electrical conducting element of relatively low resistance havin one of its ends attached and in element, and means'for pressingthe second mentioned element into contact with the first mentioned element progressively throughout its length from its attached end to its free one end of the first mentioned cluding an electrical conducting element of relativel high resistance lying in a plane, a second normally spirally curved springy electrical conducting element of relatively low resistance having one of its ends attached and in contact with one end of the first mentioned element, and means for pressing the second mentioned element into contact with the first mentioned element progressively throughout its length from its attached end to its free end.

9. A device of the character described including an electrical conducting element of relatively high resistance lying in a plane, a second normally spirall curved electrical conducting element of re atively low resistance having-one of its ends in contact with one end of the first mentioned element, and means for bringing said second mentioned element into contact with the first mentioned element progressively throughout its length, said means comprising a rotatable shaft carrying a radial arm with its free end in contact with the curved element, and means fOr rotating said shaft.

10. A device of the character described including an electrical conducting element of relatively high resistance lying in a plan., a second normally spirally curved springy electrical conducting element of relatively low resistance having one of its ends in contact with one end of the first mentioned element and means for bringing said second mentioned element into contact with the first 'mentioned element progressively throughoutits length, said means comprising a rotatable .shaft carrying a radial arm with its free end in contact with the curved element, and means for rotating said shaft.

11. A device of the character described inerty of being brought into contact with" the first mentioned element progressively throu hout its length as pressure on it 15- d throughout its len h, said meansmove comprising a rotatable sha t carrying a. radial arm with its free end in contact with said shaft. I

12. A device of the. character described including an electricalconducting-element of relatively high resistance lying in .a plane, a second normally spirally curved spring electrical element of relatively low resistance one .ofits ends in contact with one I havin end 0% the firstmentioned element, said second mentioned element having the rty of being brought into contactwithaizhe-first mentioned element progressively throughout- :the curved element, and means for rotating its length as pressure on it is moved throughout its length, said means comprising a rotatable shaft carrying a radial arm with 1ts free end in contact with the curved element, and means for rotating said shaft.

13. A device of the character described including an electrical conducting element of relatively high resistance lying in a plane, a second normally spirally curved electrical conducting element of relatively low resistance having one of its ends attached and in contact with one end of the first mentioned element, and means for pressing the second mentioned element into contact with the first mentioned element progressively throughout its length, said means compris ing a rotatable shaft carrying a radial arm with its free end in contact with the curved element, and means for rotating said shaft. 14:. A device of the character described including an electrical conducting element .of relatively high resistance lying in a plane,

a second normally spirally curved springy electrical conducting element of relatively low resistance having one of its ends attached and in contact with one end of the first mentioned element, and means for pressing the second mentioned element into contact with the first mentioned element progressively throughout its length, said means comprising a rotatable shaft carrying a radial arm with its free end in contact with the curved element, and means for rotating said shaft.

15. A device of the character described including an electrical conducting QlGli'lQHt of relatively high resistance lying in a plane, a second normally spi ally curved electrical conducting element of relatively low resist ance having one of its ends attached and in contact withoue end of the first mentioned element, and means for pressing the second mentioned element into contact with the first mentioned element progressively throughout its length from its attached end to its free end, said means comprising a 1'0- tatable shaft carrying a radial arm with its free end in contact with the curved element, and means for rotating said shaft.

16. A device of the character described including an electrical conducting element of relatively high resistance lying in a plane,

a second normally spirally curved springyelectrical conducting element of relatively low resistance having one of its ends attached and in contact with one end of the first mentioned element, and means for pressing the second mentioned element into contact with the first mentioned element progressively throughout its length from its attached end to its free end, said means comprising a rotatable shaft carrying a radial arm with its free end in contact with the curved element, and means for rotating said shaft.

17.111 a device of the class described, a rigid body of insulating material serving as a support for two electrical terminals, a filmlike conductor of high resistance carried by said body and connecting said terminals, an arm arranged to be moved over the surface of the film between one terminal and the other so as to vary the resistance by infinitesimal amounts, and a conductor of low resistance interposed'between the arm and the film so that the abrading action due to the movement of the arm will come upon sistor thus varying the resistance between said terminals by infinitesimal steps.

in. A variable electrical resistance comprising a resistor strip of conducting material; terminals for establishing electrical connection to said resistor; a contact element having a convex surface bearing upon the surface of said resistor; and means for varying the pressure between said contact element and said resistor whereby a variable area of contact between said contact element and said resistor is accomplished.

20. A variable electrical resistance comprising a resistor strip of conducting material; an insulating base to which said resistor strip is fastened; terminals for making electrical connections to the ends of said resistor; a flexible contact member in the form of a curved strip having its convex surface adjacent the surface of said resistor strip; means for flexing said contact strip and for pressing its convex surface into variable contact with said resistor strip, whereby the electrical. resistance between said terminals is varied.

21. An electrical resistance comprising a resistor in the form of a strip of insulating n'iaterial rendered conductive, an insulating base to which said resistor is fastened, ter-- minals for makingelectrical"connections to the ends of said resistor, a flexible contact member in the form of a curved strip having its convex surface adjacent the surface of said resistor; means for flexing said contact member thus pressing its convex surface into variable contact with said resistor, whereby the electrical resistance between said terminals is varied.

22. A variable resistance unit comprising a rigid base' of insulating n'iaterial, a flat fixed element of curved conliguration mounted on said base, a movable resilient element comprising a metallic strip corresponding in shape to said lixed element and intenlioned away from the latter. and means to short circuit porlions of the fixed element by means of touch contact of the movable willi the fixed element in a device of the class described, a rigid body of insulating material serving as a support for two electrical terminals, a conductor of high resistance in the form of a coating applied to a carrying medium mounted on said body and connecting said terminals, means arranged to be moved over the surface of said conductor between one terminal and the other so as to vary the r e-' sistance by infinitesimal amounts, and a conductor of low resistance interposed between said means and said first named conductor and constrained against sliding contact with the latter.

24. it variable electrical resistance com prising an insulating base, a strip of fibrous material mounted on said base, a coating of conducting material disposed upon the surface of said strip, terminals for making elecw trical connection with said coating, ametal lic contact member having a convex surface in contact witl' said conductive coating, and means for pressing said convex surface of said contact member into variable contact with said conductive coating, whereby the electricai resistance between said terminals may be varied,

25. An electrical resistance comprising a. resistor in the form of a strip of insulatto ing fibrous material having a coating there- -(-:n of conducting material, a base upon which said resistor is fastened, terminals for maltinn-electrical connection to said resistor, a contact member having a surface adjacent 4 the surface of said resistor, means for preventing a sliding, motion of said contact member with respect to the surface of said resistor, and means for pressing said contact member and said resistor into contact 59 at a controllably variable location on the resistor, whereby the resistance between said contact member and the terminals of said resistor may be continuously varied.

26. In a device of the class described, a body of insulating material, two binding posts supported thereby, a conductor of high resistance deposited on a carrying medium applied to one face of said body and connecting said binding posts, a spring of low resistance connected to one binding post and extending to a point adjacent the other binding post, said spring having a tension serving to raise it clear from the conductor of high resistance, and a manually operated device arranged to be moved longitudinally along said spring and to pres it against said conductor of high, resistance at the point Where the device engages it.

27. In a device of the class described, a base of insulating material, two binding posts carried by the base, and conducting material of relatively high resistance also carried by said base and extendin in an are from one post to the other, a spring having one end attached'to one post and extending over said are to a point adjacent the other post, the tension of said spring serving to hold it normally clear of said conducting material, an arm pivoted at the center of the arc and engaging the spring so as to press the engaged part thereof into contact with the conducting material, and a knob for turning said arm so as to cause it to sweep over said spring.

28. An electrical resistance comprising a resistor having asmooth electrical conducting surface; suitable terminals for making electrical connections to the ends of said resistor; a contact member having a surface adjacent to the surface of said resistor; a suitable terminal for making electrical connection to said contact member; means for preventing a sliding motion of said contact memberwith respect to the surface of said resistor, and means for pressing said contact member into firm contact with said resistor ata-controllablv variable location along the length of said resistor, said last mentioned means including an operating member bodily movable relatively to said resistor and over the surface of said contact member, whereby the electrical resistance between said contact member and either of the terminals of said resistor may be varied by infinitesimal steps.

29. An electrical resistance comprising an insulating base; a resistor mounted upon said base, said resistor having a smooth conducting surface; suitable terminals for making electrical connections to the ends of said resistor; a contact member having a surface adjacent said conducting surface of said resistor; means for preventing a sliding motion of said contact member upon said resistor and controllable means for establishing contact between said Contact member and said conducting surface of said resistor at a variable location along said resistor, said last mentioned means including an operating member bodily movable relatively to said resistor and over the surface of said contact member, whereby the resistance between said contact member and the terminals of said resistor may be varied by infinitesimal steps.

60. An electrical resistance comprising an insulating base; a resistor mounted upon said base, said resistor having a smooth conducting surface; suitable terminals for making electrical connections to the ends of said resistor; a contact member having a surface adjacent said conducting surface of said resistor and tangent to said conducting surface at a controllable variable location thereon; means for preventing a sliding motion of said contact member upon the surface of said resistor, and means for continuousl changing the location of tangency of said contact member upon said conucting surface whereby the electrical resistance. between said contact member and the terminals of said resistor may be varied by infinitesimal steps.

31. An electrical resistance comprising a resistor having a smooth conductin surface, a contact member in the form 0 a metal strip disposed adjacent said conducting surface, and means for pressing said-elements together, said means including an operating member bodily movable relatively to said resistor and over the surface of said contact member to vary such engagement, whereby the resistance between said contact member and the ends of said resistor may be varied in infinitesimal steps.

32. A variable resistance comprising a support, a resistance element having a smooth conducting surface mounted on said support, a flexible contact member overlying the resistance element and constrained against translatory movement, means for flexing said contact member into variable contact with said resistance element to vary the resistance of the device, and means connected with said flexing means for indicating the position thereof.

In Witness whereof, I have hereunto set my hand this 15th day of March, 1923.

DANIEL a; MOORE, 

